The field of the invention pertains generally to hydraulic control mechanisms and, in particular, to fluid control valves for the modulation of hydraulic power. More recently the development of electrorheological fluids has permitted the corresponding development of simple fluid plate valves. These valves comprise a plurality of electroconductive plates separated by insulative plates. The insulative plates include passages formed therein that lead between ports through the conductive plates. Alternating conductive plates are electrically joined in parallel whereby the application of an electric potential between the two sets of conductive plates causes an electric filed to be energized between adjacent conductive plates and through the passages in the insulative plates therebetween. With the application of the electric field a great increase in viscosity occurs in the electrorheological fluid in the passages and the valve effectively closes.
A small variety of devices have been disclosed that advantageously use electrorheological fluids. U.S. Pat. No. 4,896,754 discloses electromagnetic power transmissions and brakes that take advantage of multiple alternating flat discs in a chamber filled with an electrorheological fluid. The level of torque transmitted or braking applied is responsive to the selective and variable application of an electric filed applied to the electrorheological fluid.
U.S. Pat. No. 4,923,057 discloses the use of an electrorheological fluid in an enclosed chamber as a part of a vibration damping structure. The application of an electric field to the electrorheological fluid within the structure makes substantial change in the complex shear and tensile modulus properties of the fluid therefore the damping characteristics of the structure are greatly changed.
U.S. Pat. No. 4,819,772 discloses an automotive shock absorber filled with an electrorheological damping fluid. Electrodes about a damping fluid conduit permit an applied electric field to adjust the damping of the shock absorber. U.S. Pat. No. 4,861,006 discloses a vibration damper wherein the flow of an electrorheological fluid through an elongated orifice is adjusted by changing the apparent viscosity of the fluid with an electric field. In a similar manner U.S. Pat. No. 4,909,489 discloses the control of the flow of an electrorheological fluid through helical orifices to adjust the vibration damping of an internal combustion engine mount.
U.S. Pat. No. 4,720,087 and U.S. Pat. No. 4,733,758 are related patents disclosing vibration dampers wherein the viscosity of the electrorheological fluid is adjusted in the flow through valves in the dampers. U.S. Pat. No. 4,742,998 discloses a vibration isolation system wherein an active electronic feedback control adjusts the voltage potential applied to the electrorheological fluid in response to sensors on the vibration damper. Also disclosed is a multiple orifice valve comprising parallel conductive perforated flat plates separated by an insulated plate formed with flow channels.
The above patents disclose devices that control the flow of electrorheological fluid through simple orifices and valves or control the torque transmitted between moving plates in an electrorheological fluid bath. The control of the flow of electrorheological fluid in a sophisticated manner through sophisticated valve combinations for the control of hydraulic cylinders and rotary actuators is the goal toward which the disclosure below is directed.